3GPP Long Term Evolution (LTE) is the fourth-generation mobile communication technologies standard developed within the 3rd Generation Partnership Project (3GPP) to improve the Universal Mobile Telecommunication System (UMTS) standard to cope with future requirements in terms of improved services such as higher data rates, improved efficiency, and lowered costs. The Universal Terrestrial Radio Access Network (UTRAN) is the radio access network of a UMTS and Evolved UTRAN (E-UTRAN) is the radio access network of an LTE system. In an E-UTRAN, a wireless device such as a User Equipment (UE) is wirelessly connected to a Radio Base Station (RBS) commonly referred to as an evolved NodeB (eNodeB) in LTE. An RBS is a general term for a radio network node capable of transmitting radio signals to a UE and receiving signals transmitted by a UE. The eNodeB is a logical node in LTE and the RBS is a typical example of a physical implementation of an eNodeB. A UE may in the following also be referred to as a terminal.
FIG. 1 illustrates a radio access network in an LTE system. An eNodeB 101a serves a UE 103 located within the eNodeB's geographical area of service also called a cell 105a. The eNodeB 101a is directly connected to the core network (not illustrated). The eNodeB 101a is also connected via an X2 interface to a neighboring eNodeB 101b serving another cell 105b. Although the eNodeBs of this example network serves one cell each, an eNodeB may serve more than one cell.
The use of a so called heterogeneous deployment or heterogeneous network consisting of radio network nodes transmitting with different transmit power and operating within overlapping coverage areas, is an interesting deployment strategy for cellular networks. In such a deployment schematically illustrated in FIG. 2a, low-power nodes such as pico nodes 210 are typically assumed to offer high data rates measured in Mbit/s, as well as to provide high capacity e.g. measured in users/m2 or in Mbit/s/m2, in local areas where this is needed or desired. High-power nodes, often referred to as macro nodes 220, are assumed to provide full-area coverage. In practice, the macro nodes 220 may correspond to currently deployed macro cells 221, while the pico nodes 210 are later deployed nodes, extending the capacity and/or achievable data rates in a pico cell 211 within the macro cell 221 coverage area where needed.
In a traditional heterogeneous deployment, schematically illustrated in FIG. 2b, each pico node 210 creates a cell of its own, a so called pico cell 211. This means that, in addition to downlink and uplink data transmission and reception transmitted on the pico link 213 maintained between the pico node 210 and the wireless device 212, the pico node 210 also transmits the full set of common signals and channels associated with a cell. In an LTE context this includes the primary and secondary synchronization signals, cell-specific reference signals, and system information (SI) related to the cell, in FIG. 2b referred to as SI pico and illustrated by the dashed line cell overlying the pico cell 211
In an alternative deployment, illustrated in FIG. 2c, a terminal or wireless device 212 in the range of a pico node 210, i.e. in the subarea 214 covered by the pico node, may be simultaneously connected to both the macro node 220 and the pico node 210. To the macro node 220 covering the area 222, the terminal 212 maintains a connection or link, e.g. used for Radio Resource Control (RRC) such as mobility control. The connection or link maintained to the macro node 220 may be referred to as an anchor link 223. Furthermore, the terminal 212 maintains a connection or link to the pico node 210, used primarily for data transmission. The connection or link maintained to the pico node 210 may be referred to as a booster link 213. This approach is in the following referred to as a soft cell approach. The soft cell approach has several benefits such as mobility robustness and improved energy efficiency. The SI related to the soft cell is in FIG. 2c illustrated by a cell with a dashed line overlying the area 222. Since the macro layer is responsible for providing e.g. SI and basic mobility management, the pico node in essence only needs to be active when transmitting data to the terminal. This can lead to significant gains in energy efficiency and an overall reduction in interference as the pico nodes can be silent in periods of no data transmission activity. Macro and pico node transmission can either occur on different frequencies in a frequency-separated deployment, or on the same frequency in a same-frequency deployment.
LTE Uplink Power Control
To control the received signal power in the uplink, LTE employs uplink power control. The power-control mechanism consists of two parts:                An open-loop part where the terminal sets the approximate transmission power based on the estimated path loss between the base station and the terminal;        A closed-loop part where the network can instruct the terminal to increase or decrease the instantaneous transmission power.        
The purpose of the open-loop part is to compensate for the path loss as a terminal further away from the base station needs to transmit with a higher power than a close-by terminal if the two are to be received with the same power.
The purpose of the closed-loop part is to compensate for rapid variations in the instantaneous propagation conditions and to compensate for imperfections in the open-loop power setting. Closed-loop power control commands affecting the uplink data transmissions are included with every uplink scheduling grant.
LTE Uplink Scheduling
All LTE uplink transmissions except for random access transmissions are controlled by the scheduler. A terminal is allowed to transmit in the uplink only when it has received a valid scheduling grant from the network. An uplink grant in LTE is valid for one transport block on the Uplink Shared Channel (UL-SCH) transport channel. A transport block contains the data to be transmitted in one transmission time interval (TTI) of 1 ms length.
Data on the UL-SCH transport channel 302 of an uplink carrier or link 301 is the result of multiplexing one or more logical channels 303a, 303b. A logical channel 303a, or 303b, is characterized by the type of information transmitted. For example, one logical channel 303a could be used for RRC signaling associated with mobility management while another logical channel 303b is used for the user data. Although the eNodeB scheduler controls the transport block size and the associated transmission parameters such as the modulation scheme of a scheduled mobile terminal, the terminal is responsible for selecting from which logical channels the data is taken. The terminal autonomously handles logical channel multiplexing according to rules, the parameters of which can be configured by the network. This logical channel multiplexing is illustrated in FIG. 3, where the eNodeB scheduler controls the transport format and the mobile terminal controls the logical channel multiplexing.
Each logical channel has a corresponding Radio Link Control (RLC) buffer for buffering its data. Data from multiple logical channels of different priorities can be multiplexed into the same transport block according to a configurable rule. As illustrated in FIG. 3, the Medium Access Control (MAC) offers services to the RLC in the form of logical channels. MAC also handles Hybrid Automatic Repeat Request (HARQ) retransmissions and uplink and downlink scheduling. The Physical Layer (PHY) handles e.g. coding/decoding and modulation/demodulation and offers services to the MAC layer in the form of transport channels.
The simplest rule for multiplexing data from multiple logical channels into a single transport block would be to serve logical channels in strict priority order. However, this may result in starvation of lower-priority channels, as all resources would be given to the high-priority channel until its transmission buffer is empty. Typically, an operator would instead like to provide at least some throughput also for low-priority services. Therefore, for each logical channel in an LTE terminal, a prioritized data rate is configured in addition to the priority value. The logical channels are then served in decreasing priority order up to their prioritized data rate, which avoids starvation as long as the scheduled data rate is at least as large as the sum of the prioritized data rates. Beyond the prioritized data rates, channels are served in strict priority order until the grant is fully exploited or the RLC buffer is empty. Such a prioritization is schematically illustrated in FIGS. 4a-c. The content from two logical channels LC1 and LC2, indicated by the stacks LC1 and LC2 respectively, is to be transmitted in decreasing priority order up to the prioritized data rate indicated by 403. LC1 has the highest priority. The scheduled data rate is indicated by the line 401. What is actually transmitted is indicated by stack 402.
LTE Carrier Aggregation
LTE Rel-10 supports carrier aggregation where up to five Component Carriers (CC) can be aggregated to support higher data rates than what would be possible with a single carrier. Scheduling, HARQ retransmissions and PHY processing are handled independently for each CC 501a-c, as schematically illustrated in FIG. 5. Several logical channels 503a, and 503b, are multiplexed and the resulting output is distributed across the scheduled CCs. Data from one logical channel 503a may be transmitted on one or more CCs 501a-c depending on the payload sizes scheduled for each of the CCs and the logical channel prioritization described above with reference to FIG. 4a-c. 
In LTE, there is one primary CC and one or more secondary CCs. Uplink control signaling on PUCCH, such as HARQ feedback, and Channel Status Indicator (CSI) reports, is transmitted on the primary CC only, irrespective of which downlink CC(s) that were used for downlink data transmission. Uplink power control is performed independently per uplink CC.